A trocar generally comprises two major components, a trocar tube and an obturator. The trocar tube or cannula is inserted through the skin. Access is gained through to a body cavity so that endoscopic, laparoscopic or arthroscopic surgery may be performed. In order to penetrate the skin, the distal end of the trocar tube is placed against the skin and an obturator is inserted through the tube. By pressing against the proximal end of the obturator the point of the obturator is forced through the skin until the obturator enters the body cavity. At this time, the trocar tube is inserted through the perforation made by the obturator and the obturator is withdrawn, leaving the trocar tube as an accessway to the body cavity.
It has been found that often a great deal of force is required to cause the obturator point to penetrate the skin and underlying tissue. When the point finally breaks through this tissue, resistance to penetration is suddenly removed, and the obturator point can suddenly reach to penetrate internal organs of the body, which may cause lacerations and other injury to the internal organs. To avert this danger to the patient, trocars have been developed which carry a spring-loaded tubular shield within the trocar tube and surrounding the obturator. The distal end of the shield presses against the skin as the obturator point penetrates the body, until the obturator has formed a perforation with a diameter sufficient to allow the safety shield to pass through. At that time the resistance of the tissue to the spring-loaded shield is removed, and the shield will spring forward to extend into the body cavity, surrounding the point of the obturator. The shield thus protects the internal body organs from inadvertent contact with the point of the obturator. A trocar including such a safety shield is described in U.S. Pat. No. 4,535,773, for example.
The tubular shield in such a trocar will, however, require the incision formed by the obturator to extend to a considerable diameter before the resistance of the tissue pressure has been sufficiently decreased to allow the safety shield to spring forward. It is only when the incision attains the diameter of the shield that the shield is fully able to spring into the body cavity. When the obturator employs a long, tapered cutting tip, this tip must extend a significant distance into the body before the incision is sufficiently enlarged to release the safety shield. It would therefore be desirable to provide a safety shield which will spring forward to shield the obturator tip as soon as possible after entry is gained to the body cavity.
In accordance with the principles of Deniega, U.S. Pat. No. 5,066,288, a safety shield for a trocar obturator is provided which exhibits a rounded, bullet-shaped distal end. A slot is formed in this distal end which corresponds to the geometry of the obturator tip, through which the tip extends during perforation of the skin. With this distal end conforming to the geometry of the tip, a smooth transition is provided from the tip to the distal end of the shield, enabling the shield to closely follow the obturator tip through the tissue. The rounded distal end will press against the skin and tissue in close proximity to the periphery of the incision as it is formed, and will aid in the enlargement of the incision to enable the shield to spring forward nearly as soon as entry is gained into the body cavity.
One desirable function of such a trocar is for the obturator to slide smoothly within the trocar tube during both insertion and retraction of the obturator. Opposing this need is the necessity to form the obturator to be nearly the same diameter as the tube, so that the tissue perforation will be the size of the tube. Thus, tolerances are generally tight between the diameter of the obturator and the inside diameter of the trocar tube. A further complication is provided by the valve at the proximal end of the trocar tube, which is needed to seal the proximal end during removal of the obturator when the trocar tube and body cavity are insufflated with gases. The valve, which generally takes the form of a hinged flap or trumpet valve, is spring-loaded to bear against the obturator, thereby assuring that the valve will close automatically upon withdrawal of the obturator from the trocar tube. As the valve bears against the obturator it will frictionally disrupt the entry and withdrawal of the obturator. As a result of these tolerance problems, heretofore there has not been an obturator which corresponds identically to the shaft of the trocar cannula, and wider than the inner dimension of the safety shield in which the obturator slides.
Further patient safety would be provided by preventing the sudden extension of the obturator into the body cavity as the obturator tip fully penetrates the tissue. In accordance with yet another aspect of Deniega '688, means are provided which permit only incremental advancement of the obturator as tissue penetration proceeds. Such incremental advancement is provided by a ratchet or screw mechanism, for instance. Yet, this has not alleviated the problem of having an obturator tip with only minimal exposure past the edge of the safety shield at all positions of the safety shield distal end.